In the past, a polybutadiene in which a portion of double bonds of the side chains are silylated is known. For example, a curable composition containing a polybutadiene in which silyl groups are added to a portion of carbon-carbon double bonds of the side chains and a carbonaceous material is suggested in Patent Document 1. Concretely, a curable composition containing a polybutadiene in which 20.5% or 25.2% of carbon-carbon double bonds of the side chains are triethylsilylated is disclosed. Since the cured product obtained from the curable composition has excellent heat and water resistance, conductive properties, and the like, applications such as a separator for fuel cell, an electrode, an electromagnetic shield, a heat release material, an assembly for a battery, and the like, are proposed.